Storage battery separator



"of the resultant product. be either too brittle or too soft, in whichevent it was STORAGE BATTERY SEPARATOR Edward R. Dillehay, Glen Ellyn,and Gordon H. Fernald, Geneva, Ill.

N Drawing. Original application August 11, 1948, Se-

rial No. 43,767. Divided and this application May 17, 1954, Serial No.432,904

1 Claim. (Cl. 136146) Our invention relates to separators for usebetween the plates of electric accumulators of the lead-acid type.

This application is a division of application Serial No. 43,767, filedAugust 11, 1948, now abandoned.

It is an object of our invention to provide a novel storage batteryseparator and mode of manufacture both of which are of low cost.

-It is an object of our invention to provide a storage battery separatorwhich has improved characteristics over those hitherto known and inparticular a separator which is acid-proof, tough, non-brittle, stifienough to permit easy handling in the building of the accumulator, andhas a high porosity in spite of a minute pore size.

It is an object of our invention to provide a storage battery separatorwhich may be handled dry, but which is readily wet by storage batteryacid so as to possess a low resistance.

These and other objects of our invention, which will be set forthhereinafter or will be apparent to the skilled worker in the art, weaccomplish in that article and composition and by that procedure ofwhich we shall now describe an exemplary embodiment.

In the past it has been suggested that storage battery separators couldbe made by compounding a thermoplastic binder with a powdery substancewhich could be leached out or otherwise removed after the compositionhad been formed into sheets. Some successful storage battery separatorshave been made in this way but the process and product have presented anumber of difficulties. It was a problem to incorporate into thecomposition a sufficient quantity of the removable substance to give thedesired porosity without destroying the strength The plastic body tendedto characterized by cold flow and substantial shrinkage duringmanufacture. The processes hitherto employed for securing porosity werealso complicated and expensive.

In the practice of our invention we have discovered that the desiredqualities in the final product may be attained through the use of acombination of thermoplastic and thermosetting substances as hereinaftertaught; that a high degree of porosity may readily be attained by themethods taught herein providing the composition is given particularcharacteristics; and that toughness and strength may be achieved alongwith stiffness and freedom from disadvantageous cold flow, in aseparator made from a composition for which we shall now give anexemplary but non-limiting formula:

Salt (220 mesh) 1,700

The above parts are by weight. We shall now discuss the ingredients ofthis composi- States Patent 0 "ice tion and the manner in which theycoact to the desired end.

The Vinylite VYNS is a copolymer of vinyl chloride and vinyl acetatecontaining approximately 7% of the acetate and having a high molecularweight. It contributes toughness to the storage battery separator. Thereare many variations of the vinyl compounds, and we may employ any ofthem which are tough polymers. We may employ straight vinyl chloride,copolymers of vinyl cloride and other substances, such as vinylidinechloride or a copolymer of vinyl chloride and vinyl acetate containing ahigh percentage of the acetate. preference is for the specific copolymerin the formula given above, as producing the best general properties inthe separator.

The phenol furfural resin is formed by polymerizing phenol and thealdehyde in ways known in the art. As the resin is compounded with theother ingredients in the formula given above, we prefer to have it in arather thin condition, i. e. with a viscosity substantially in the rangeof 500 to 1000 centipoises. Other thermosetting resins can be employedby us in the separator providing they are acid-proof in character andare compatible with the vinyl thermoplastic. For example, a one-stage ortwo-stage phenol formaldehyde resin is satisfactory prophenol furfuralresin because of its superior acid resistance, good working qualitiesand excellent com-" patibility with the other ingredients of thecomposition. The sulfonated castor oil we prefer to employ is the.so-called 75% grade which contains that quantity of the pure sulfonatedoil, the other 25% being impurities suchas water. The sulfonated castoroil is a very important ingredient of our composition. It is not only awetting agent, but also a'plasticizer, permitting us to incorporate verylarge amounts of salt to obtain good working qualities. Without thesulfonated castor oil or with a wetting agent which cannot serve as aplasticizer, no more than about 1200 parts of salt could be incorporatedinto a composition otherwise of the formula given above, and

even with 1200 parts the compound became very dry and 'diflicult tohandle and also brittle after the solvent had been removed and prior tothe extraction of thesalt. Under the extending and plasticizing actionof the sulfonated castor oil, we are able to add so large an amount ofsalt as to lower the resistance of the separator to practically anyvalue desired.

With the amount of salt given in the formula above, we obtain a niceworking composition for the extraction and calendering operations, whichcomposition is nonbrittle after the solvent has been removed and has theI right consistency for the finished separator.

dried, but when they are again immersed in battery acid,

they become wetted immediately and regain their original low resistance.With the incorporation of the sulfonated castor oil into thecomposition, no treatment of the final separators to render themwettable is required.

Cellosolve acetate" is ethyl glycol monoethyl ether acetate and iscompatible with water. It is employed by us as a solvent and initialextender of the binder sub- Our We prefer the 3 stances whichfacilitates the mixing in of a large quantity of salt. We can, however,use a variety of other solvents for the purpose, such as methyl ethylketone, furfural, acetone, any of the ketone-type. solvents, andmixtures of these substances. The solvent employed should be one easilyremoved and relatively inexpensive.

The salt contemplated in the above formula is preferably sodium chlorideground to a fine powder. It has the advantage of great cheapness, isreadily removed by leaching with water, and is completely satisfactoryin every way. We may employ any other soluble inorganic salts readilyand completely removable by leaching, as well as leachable substanceswhich are not inorganic salts, such as pulverized sugar or pulverizedurea crystals. Our preference is for the sodium chloride for reasonsgiven above. More expensive materials would need to be recovered inorder to make their use economical, while a substance requiring the useof a special solvent for leaching entails an additional expense.

Any leachable substance used for porosity should be finely divided. Wegrind our salt to 200-mesh size or smaller. We have found that amaterial, all of which will pass through the standard screenof 200meshes to the inch is fine enough, but a smaller pore size can readilybe obtained by grinding to still smaller sizes.

In processing our composition and separators, we combine theingredients, such as those set forth in the formula above, in a suitablemixer at a temperature preferably around 180 F. to 200 F. Any ribbon orblade-type mixer may be employed, or we may use a pressure mixer such asthe Banbury. In our preferred method of mixing the vinylite in the formof a powder is thoroughly blended with the 200 mesh salt. Thethermo-setting resin is separately dissolved in the solvent, with orwithout the addition of the plasticizer. Then the'liquid ingredients areadded to the dry pre-blend first mentioned.

Mixing is continued until the composition is homogenous. The finishedcomposition has a soft dough-like consistency, and is formed into thinsheets in any suitable way. For example, the composition may becalendered in a two-roll calender against a steel plate which is groovedto form the desired ribs on the separator. It is preferable and lessexpensive in large-scale production to extrude the material from anorifice in an extrusion machine, which orifice is shaped to provide acontinuous, thin, sheet-like ribbon with preformed ribs.

From the extrusion machine or other means whereby the composition isformed into sheets or continuous lengths, it passes to an oven where thesolvent or solvents are eliminated by vaporization, and thethermosetting resin is set up. The solvent may be recovered, foreconomy. The temperature and time of treatment will depend upon thenature of the resin, and since they are within the capabilities of theskilled worker to select, they form no necessary limitation on thisinvention.

After drying and curing, the sheets or lengths are subjected to awashing operation, either continuous or batch, in which they areimmersed in moving water at a temperature preferably around to F. Thewater should be flowing so as to be renewed when it becomes laden withsalt, and it may further be agitated with air if desired.

When the salt has been removed from the separator material, it will bein a porous condition, and may be dried. It is then cut apart intoindividual separators, as may be required, which are packed forshipment.

Our separators have about one-fourth the resistance of the so-calledmicroporous rubber separators, do not shrink unduly when cooled, andhave a very satisfactory zero discharge test.

Modifications may be made in our invention without departing from thespirit of it. Having thus described our invention in an exemplaryembodiment, what we claim as new and desire to secure by Letters Patentis:

A storage battery separator which is a sheet-like, highly porous bodyconsistingof the following ingredients in substantially the proportionsindicated:

